As a short-range wireless local area network communications technology, a Wireless Fidelity (WiFi) technology is widely used because of its advantages such as a free spectrum and a high transmission rate. At present, WiFi access points (AP) are disposed in many public places such as airports, restaurants, and conference rooms. A user can connect a terminal with a WiFi network interface to an AP for low-cost or free network access.
Before sending an association request message to the AP, the terminal sends a probe request message to the AP. The probe request message carries device information of the terminal, for example, device capability information, supported rate information (Support rates), extended supported rate information (Extended Supported Rates), and vendor-specific information (Vendor Specific). These pieces of device information do not change in a normal case, that is, these pieces of device information that are carried in the probe request message that is sent before the terminal associates with the AP remain unchanged for a long time. Among these pieces of information, a single piece of information is not globally unique among different devices. However, a combination of one or more pieces of information in the information may become “fingerprint” information of a device. It is likely that the “fingerprint” information can uniquely identify the device to a great extent in a local area or even in an entire network. Therefore, an eavesdropper that receives the probe request message over an air interface and analyzes the “fingerprint” information message carried in the message is able to track the device and obtain privacy information of the user. For example, the eavesdropper obtains a frequently visited place and visiting time of the user, so as to obtain the privacy information, such as a life habit and a social relationship, of the user by analyzing a great amount of data.